Resolved line profiles of atomic oxygen resonance lamps used in the upper atmosphere

Line profiles of the 130-nm OI(³P-³S) resonance triplet emitted by r.f. excited helium/ oxygen lamps have been resolved using a photoelectric echelle spectrometer. These profiles have been reproduced using a self-absorbed double-Gaussian spectral distribution in which the relative amplitudes of the Gaussian components are functions of the oxygen and helium partial pressures in the lamps. Reasons for the form of the observed spectral distribution are suggested and the importance of the spectrometer measurements to studies of atomic oxygen in the upper atmosphere involving this type of lamp illustrated.     

Existentially closed structures and Jensen’s principle

AssumeV=L, or even ◊ _{M 1}, there is no uncountable locally finite group which can be embedded in every uncountable universal locally finite group. Similar results hold for existentially closed groups and division rings. Partially supported by NSF.     

Etching models for A {111} diamond surface: Calculation of trigon slopes

A mathematical analysis of the etching of {111} diamond surfaces is developed. The slopes of etch pit faces are computed in terms of the specific rate constants, k₂ and k₃, for removal of two- and three-bonded atoms along 〈1̄10〉 steps and the specific rate constant, k_d, for step nucleation at the central initiating defect. Interactions between neighboring steps are neglected. Two limiting etching regimes are found, i.e., one in which the step velocity increases linearly with step length and a regime of constant step velocity. If k_d is limited by a no overhang criterion, i.e., nucleation of a new step cannot occur until the prior step has moved out of the way, k_d and etch pit slope are functions of the size of the initiating defect. This allows etch pits of vastly different slope to be formed at the same $\text{k}{}_2\text{k}{}_3$ ratio. Point bottom pits with shallow (less than 2°) slopes form from small initiating defects, e.g., dislocation outcrops. At the same $\text{k}{}_2\text{k}{}_3$ ratio flat bottom pits with steep (70° 32') outer faces are formed by etching from large shallow defects, e.g., ring cracks or inclusions. Some preliminary conclusions are drawn about the chemical environment present during the latter stages of diamond genesis.     

Exo-pi-bonding to an ortho-carborane hypercarbon atom: systematic icosahedral cage distortions reflected in the structures of the fluoro-, hydroxy- and amino-carboranes, 1-X-2-Ph-1,2-C2B10H10 (X=F, OH or NH2) and related anions

The structures of derivatives of phenyl-ortho-carborane bearing on the second cage hypercarbon atom a pi-donor substituent (F, OH, O-, NH2, NH- and CH2-) were investigated by NMR, X-ray crystallography and computational studies. The molecular structures of these compounds, notably their cage C1-C2 distances and the orientations of their pi-donor substituents (OH, NH2, NH- and CH2-) show remarkable and systematic variations with the degree of exo pi-bonding, which varies as expected with the pi-donor characteristics of the substituent.     

Big macrocyclic assemblies of carboranes (big MACs): synthesis and crystal structure of a macrocyclic assembly of four carboranes containing alternate ortho- and meta-carborane icosahedra linked by para-phenylene units

The macrocyclic compound, [1,2-C₂B₁₀H₁₀-1,4-C₆H₄-1,7-C₂B₁₀H₁₀-1,4-C₆H₄]₂ (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)-ortho-carborane. The X-ray crystal structure of 5·C₆H₆·6C₆H₁₂ was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic C_s and local C_2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D_2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol⁻¹ higher in energy than the C_2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful.     

Sulfur-Doped n-Type Diamond: Preparation and Electrochemical Properties

Films of sulfur-doped synthetic diamond are chemical-vapor-deposited using codoping with sulfur and boron. The sulfur in diamond is detected with particle-induced x-ray emission (PIXE), x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). Electrochemical and thermoelectric measurements show that the sulfur-containing diamond films grown in gas phase lean in boron are n-type, whereas those grown with higher boron content are overcompensated, hence, p-type. Electrochemical properties of the n-type diamond films are studied for the first time using methods of electrochemical impedance, open-circuit photopotential, and voltammetric curves in Fe(CN)₆ ^3-/4- solutions. A mechanism of boron-stimulated sulfur incorporation into diamond and the nature of donors thus formed is discussed.     

LaI2@(18,3)SWNT: the unprecedented structure of a LaI2 "Crystal," encapsulated within a single-walled carbon nanotube.

The novel crystallization properties of nano-materials represent a great challenge to researchers across all disciplines of materials science. Simple binary solids can be found to adopt unprecedented structures, when confined into nanometer-sized cavities, such as the inner cylindrical bore of single-walled carbon nanotubes (SWNT). Lanthanum iodide was encapsulated within SWNTs and the resulting encapsulation composite was analyzed using energy-dispersive X-ray microanalysis (EDX) and high-resolution transmission electron microscopy (HRTEM) imaging techniques, to reveal a one-dimensional crystal fragment, with the stoichiometry of LaI2, crystallizing in the structure of LaI3 with one third of the iodine positions unoccupied. A complete characterization of the encapsulation composite was achieved using an enhanced image restoration technique, which restores the object wave from a focal series of HRTEM images, providing information about the precise structural data of both filling material and host SWNT, and thereby enabling the identification of the SWNT chirality.     

Use of a highly effective intramolecular Pauson-Khand cyclisation for the formal total synthesis of (±)-α- and β-cedrene by preparation of cedrone

The cedrene carbon skeleton was directly and efficiently assembled from a simple monocyclic precursor by the strategic use of a high yielding intramolecular Pauson-Khand cyclisation reaction. A small number of further synthetic manipulations provided a concise formal total synthesis of α- and β-cedrene. The cyclisation precursor was readily prepared, with a stereoselective ketone alkenylation selectively providing the olefin required for efficient access to the natural target.     

Modeling highly branched structures: Description of the solution structures of dendrimers,polyglycerol, and glycogen

We show that Random Branching Theory (RBT) accurately describes the structures of various synthetic and natural highly branched polymers in solution. We test the theory against data taken from the literature, including radii of gyration of glycogen, hyperbranched polyglycerols, and polyamidoamine dendrimers and the small‐angle X‐ray scattering profiles of these same dendrimers. In particular, all these polymers can be described adequately by sequentially branching units, packed together in a random close packing arrangement. Combined with previous tests against experiments and computer simulations, the evidence presented here shows that RBT is a simple, but surprisingly useful, theory of highly branched polymers' solution structure. We suggest that it is sufficiently powerful to be useful in the design of new polymers. Our most surprising conclusion is that random attachment of component parts produces a good model of regularly branched polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1525–1538, 2011